does it sound when you are hitting boost? because if its the sound im thinking of then we got a problem...i have my stock fan still installed and no problems with it...
if its the sound im thinking then your probably starting to develop a gap in between your turbo and your manifold due to the bolts getting loose..
then you have the time and your car is not hot, take off the heatshield to the mani using 10mm socket and reach down to the flanges where the turbo meets the manifold, and feel to see if all 4 nuts are there... if not then thats your sound..
i had a post a while ago describing my situation maybe it'll help you out...GL..
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